The present invention relates generally to providing seals along shafts of medical devices by means of radiant energy and is especially suitable for seals of catheter balloons onto catheter shafts. Various aspects of the invention include a radiant energy sealing apparatus as a means for rapidly forming finished medical device products while precisely and automatically aligning the energy emission at desired locations on the product, a method of manufacturing these medical devices through the use of shrink tubing, and a particularly advantageous shrink means for use in conjunction with the apparatus and the method.
Balloon catheters and other medical devices having overlying cylindrical members must develop smooth and secure annular seals or bonds between different assembly parts. In the case of balloon catheters, the balloon is initially an assembly part in the form of an overlying cylindrical member that has to be very securely sealed onto the cylindrical shaft of the catheter near its head. Upon completion of the catheter, the balloon is inflatable so as to make possible, in the case of a Foley catheter for example, retention of the catheter head within the bladder of a patient whereby body fluids can be drained therefrom through the urethra via a lumen through the catheter shaft. Seals for this purpose should be accurately formed, should be as smoothly tapered as possible, and should present very low adulteration risks in order to minimize the chances of patient trauma and urinary tract irritation.
Long used in manufacturing such catheters and the like has been natural rubber latex which is low in cost and has the assembly advantage that the balloon and shaft can be molded in one piece, but which material has come under criticism because of the belief that when devices made therefrom are left within the patient for longer than a day or so, reactions develop with tissue adjacent the catheter that can lead to considerable patient discomfort.
Manufacturing such medical devices from materials other than natural rubber latex or the like generally necessitates a two-piece assembly of the balloon cylinder to the catheter shaft, which assembly can be carried out by such general approaches as bonding the balloon to the shaft with an adhesive, by heat sealing a thermoplastic balloon to a thermoplastic shaft, or by combining adhesives with heat sealing. Adhesives are used for silicone rubber devices but they are usually best avoided because of the additional handling steps and time needed during manufacture and because of potential adulteration risks associated generally with the use of adhesives in medical equipment. Radio frequency heating is generally unsatisfactory because of the need to contact the parts being sealed which deforms the surface and does not allow ready transfer of heat to the interface between the parts, and because of non-uniformity of surface and seal. The use of radiant energy and thermoplastic materials for medical devices to be heat sealed are mentioned in U.S. patent application Ser. No. 853,738, filed Nov. 21, 1977, and Ser. No. 900,965, filed Apr. 28, 1978, the disclosures thereof being incorporated by reference herein.
Heretofore, heat sealing techniques, even those avoiding contact between the surface being sealed and the bonding apparatus, have not proven entirely successful. Non-contact radiant energy sealing has been observed to be generally inconsistent in its ability to thoroughly and securely seal balloons to the shafts of catheters along the entire annular extent of the seals. A catheter balloon must have no weak points at which the fluid under pressure will slowly dissipate from the balloon when in the environment of the body tissue, which can lead to patient discomfort and occasionally dislodgement from its intended location within the body of the patient.
The present invention provides a method, a shrink tubing means, and an apparatus for forming the types of seals required to meet these needs. Method steps in accordance with this invention include the use of shrink tubing to hold the balloon in place and simultaneously assist in shaping smooth seals, which method includes preshrinking the shrink tubing into place. Preferably, in close association with this method is a shrink tubing means that has been discovered to be especially useful in connection with the forming of extremely secure and consistent sealing throughout the entire annular extent of the radiant energy seal. The apparatus of the present invention provides a uniform annular band of radiant energy to be supplied according to the method of this invention, which radiant energy is transmitted through the shrink tubing means according to this invention. In a preferred aspect of the invention, tinted lengths of shrink tubing are placed over the annular locations to be sealed along the catheter shaft, the shrink tubing is preshrunk along a predetermined length thereof, and the head end of the catheter is then inserted into the apparatus whereupon it is automatically aligned to the proper location along the shaft, radiant energy is applied, and the apparatus then automatically aligns the shaft to the next location therealong, after which further heat sealing treatment is carried out in order to complete the seal at another location along the shaft.
It is accordingly a general object of the present invention to provide an improved method, means, and apparatus for preparing medical devices having overlapping members to be sealed together.
Another object of the present invention is an improved apparatus, means and method for assembling a cylindrical balloon to a balloon catheter or the like in a manner that forms a uniform and secure annular seal that is smoothly tapered for the avoidance of unnecessary trauma to the patient being treated with the device.
Another object of this invention is an improved method, means and apparatus for forming an annular seal between thermoplastic materials, which seal is extremely secure and smoothly tapered as between a cylindrical shaft and an overlying cylindrical balloon.
Another object of the present invention is an apparatus and its associated method whereby precise locations along a cylindrical shaft are subjected to an annular ring of radiant energy and automatically indexed to the next location.
Another object of the present invention is an improved shrink tubing means for forming radiant energy heat seals that are especially secure and well tapered in association with the method of this invention, which means precisely transmits and directs appropriate heat sources in order to optimize the effectiveness of the heat source in producing an extremely secure and consistent seal.
Another object of the present invention is an improved apparatus, method and means for producing balloon catheters and the like with minimal assembly operator involvement and in an extremely short length of time to minimize the amount of heat conducted away to the material surrounding the bond zone, leading to less heat distortion and possible chemical changes in the material.